Radar/Transcript
Transcript Text reads: The Mysteries of Life with Tim and Moby A boy, Tim, and a robot, Moby, are in their backyard. Tim throws a baseball, and Moby measures its speed with a radar gun. The screen on the radar gun reads: 44 mph. MOBY: Beep. Moby takes his turn throwing the baseball. It moves through the air very slowly. Tim measures its speed with a radar gun. The radar gun's screen reads: 1 mph. TIM: Weird. Tim taps the radar gun with his fingers. Text appears on its screen. Tim reads the text aloud. TIM: Dear Tim and Moby, What does radar do, and how does it work? From, Tom. Radar is an acronym that comes from Radio Detection and Ranging. An animation shows a huge radar dish. The dish is emitting a signal. TIM: It's used to get information about distant objects, like distance, speed, direction, and shape. Four images depict the radar dish gathering the types of information Tim names. TIM: Radar gathers this information by bouncing radio waves, a type of electromagnetic radiation, off of objects. An animation shows a large radar dish bouncing radio waves off of an airplane flying overhead. TIM: It's used for all kinds of purposes, like air traffic control, police monitoring of cars' speeds, weather forecasting, and navigation on ships. Images show a flying plane, a policeman running radar on a moving car, a cloud in a thunderstorm, and a ship in the ocean. MOBY: Beep. TIM: Well, there are lots of different kinds of radar, but any radar system is made up of four parts, a transmitter, which creates radio waves and amplifies their power. An animation shows a transmitter sending radio waves. TIM: An antenna which sends out waves and receives the ones that have bounced off something. An animation shows the transmitter hooked to a radar-dish antenna. The antenna is transmitting and receiving radio waves. TIM: A receiver, which analyzes the returning radio waves, or echoes. An animation shows a receiver hooked to the antenna and transmitter. The receiver is analyzing the signals it receives. TIM: And a display, which lets people see the information the radar system has collected. An animation shows a display screen. It is attached to the receiver, antenna, and transmitter. A soldier observes the screen as it displays information. MOBY: Beep. TIM: You don't get it? Don't you have a built-in radar system? MOBY: Beep. Moby frowns. TIM: You didn't read your own user's manual? Moby! Okay, here's how radar works. The antenna sends bursts of radio waves out in all directions. An animation shows a spinning radar dish transmitting radio waves as it rotates. TIM: When those waves hit something, some of them will bounce back toward the antenna. It's the same way that light bounces off a mirror or your voice echoes off the side of amountain. An image shows Moby shining a flashlight into a mirror. An animation shows Moby facing a mountain and beeping loudly, with the beep echoing back to him. TIM: Anyway, electromagnetic waves move at a constant speed, the speed of light. So, by measuring the time between when the wave was sent out and when it returns to the antenna, the radar system can get a pretty good sense of an object's location. An animation shows a radar dish bouncing a signal off of an airplane flying overhead. MOBY: Beep. TIM: Radar systems can tell how fast a target is moving because of something called the Doppler shift. If you bounce radio waves off a moving object, that object changes the frequency of those waves when they bounce back. If the object is moving toward the radio antenna, the frequency of the waves will be compressed. And if it's moving away from the antenna, the frequency of the waves will be enlarged. Animations compare a car driving toward a radar antenna with a car driving away from a radar antenna. The frequencies of the waves differ as Tim describes. TIM: By judging the changes in the wavelength, the radar antenna can detect how fast an object is moving, and in what direction. MOBY: Beep. TIM: The earliest radar systems were developed by various scientists around the world in the first few decades of the twentieth century. Instead of pulses, they shot out continuous streams of radio waves. An animation shows an early form of radar being used to detect a ship at sea. TIM: They could detect the presence of an object, but not it's size or speed. During World War Two, the British developed a far more advanced radar system to detect German bombers. The British system used pulse radar. It transmitted waves in short bursts, receiving echoes in the time between the transmissions. An animation shows a 1940s-era land-based pulse radar system. TIM: These days, radar's been refined to do much more complex things. For instance, archaeologists use ground-penetrating radar to explore sites that are still buried underground. An animation shows an archaeologist shooting radar into the ground beneath him. The radio waves bounce from underground ruins back toward the archaeologist. TIM: And satellites use radar to make exact maps of the surface of the earth or other planets. Animations show satellites above Earth and above a moon of Saturn. Both satellites bounce radio waves off of the bodies beneath them. MOBY: Beep. TIM: Yeah. In fact, spacecraft from Earth have used radar to map the surfaces of lots of planets and moons in our solar system. MOBY: Beep. Moby looks nervous. TIM: Uh, let's see. Venus, Mars, the Moon, Titan. Rockets ignite beneath Moby's feet. He flies upward. TIM: Huh. I wonder what that was all about. Category:BrainPOP Transcripts